spring Thymeleaf：如果属性和属性存在，则显示文本
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Thymeleaf: show text if the attribute and property exists
提问by James
Is there a simple way in thymeleaf to show the content of an attribute property if the property and the attribute exist? If there's an attribute "error" with a property "summary" in my html page, I'd like to show it:
如果属性和属性存在，thymeleaf 中是否有一种简单的方法来显示属性属性的内容？如果在我的 html 页面中有一个带有属性“摘要”的属性“错误”，我想显示它：
<span th:text="${error.summary}">error summary</span>
If there is no attribute "error" the following error is raised:
如果没有属性“error”，则会引发以下错误：
org.springframework.expression.spel.SpelEvaluationException: EL1007E:(pos 0): Field or property 'summary' cannot be found on null
org.springframework.expression.spel.SpelEvaluationException: EL1007E:(pos 0): Field or property 'summary' cannot be found on null
Currently I'm using the following approach, which just seems too complicated.
目前我正在使用以下方法，这似乎太复杂了。
<span th:if="${error != null and error.summary != null}"><span th:text="${error.summary}">error summary</span></span>
Is there a simpler way to achieve that?
有没有更简单的方法来实现这一目标？
回答by tduchateau
Sure! Since the processor associated with the th:ifattribute has a higher precedencethan the one associated with the th:textattribute, it will be evaluated first. Thus you can write:
当然！由于与th:if属性关联的处理器的优先级高于与属性关联的处理器th:text，因此将首先对其进行评估。因此你可以写：
<span th:if="${error != null && error.summary != null}" th:text="${error.summary}">Static summary</span>
You could even shorten it using:
您甚至可以使用以下方法缩短它：
<span th:text="${error?.summary}">Static summary</span>
But I think in this case, whether the summary exist or not, the span tag will be created, which is a bit ugly.
但是我觉得在这种情况下，无论是否存在summary，都会创建span标签，有点难看。
See more info about conditional expressions here.
在此处查看有关条件表达式的更多信息。
